Quite a large number of types of fish are commonly sold for consumption in the form of boneless fillets. These fillets are obtained by cutting the fish off along each side of the bones, so that a limited number of large pieces, slices or strips of boneless fish per filleted fish are obtained. Filleting takes place either on a small scale by cutting away the fish pieces by hand with a knife which may or may not specially provided for the purpose, or on a large scale with appliances or machines which automatically cut the fish fillets away from the bones. With each of these machines or appliances an effort is made to cut away as much of the fish as possible as fillets, in order to ensure that the proportion of the fish left behind on the bones--and involving a loss--is kept as small as possible. It is, however, impossible to remove all the fish during filleting, either by hand or mechanically, because the fillets are cut off along a straight line which does not run up against the bones of the fish at all points. Consequently, after filleting, apart from the fillets themselves, a fish bone to which a certain quantity of fish still remains clinging is obtained. This quantity of fish is situated mainly along the main bone of the fish, which is thicker than the side bones and consequently forms an angle with those side bones which is inaccessible for the filleting knife, lying in the lengthwise direction of the main bone. The object is then to prevent this part of the fish from being lost. A number of processes and machines with that object are also known, by means of which this quantity of fish is removed from the bones for processing into a saleable fish product.
The patent DE-PS-2823249 (with priority in the United Kingdom GB-23347/77) describes a machine and corresponding process in which the bond between bones and fish is weakened in the first instance through heating, and the fish is then removed from the bones by means of liquid jets or air jets, this machine also being provided with a beating device for further weakening the bond between the bones and the fish mechanically after heating.
The end product is a quantity of boneless fish which is made up of small pieces and is more or less cooked, which then cannot, of course, be sold as a fillet, but has to be processed further to a fish product which in its composition does not require the fish to have its original structure (e.g. pies and the like).
French patent FR-8703464 describes another machine and process by which the side bones are cut off along both sides of the main bones, by having the bones (with the remaining fish parts after filleting) carried along on a conveyor belt, at right angles to the direction in which two circular, rotary knives situated along either side of the path of the main bone are disposed. This process then permits a further recovery-not constituting part of this patent-of the fish on the side bones. Here again, fish in the form of fillets as the end product is not obtained, since the side bones of the fish still form part of the parts cut off and require a further treatment.
In the patent application DE-AS-2714101 a machine equipped as described above is improved with a device which automatically adjusts the distance between the individual knives of the cutting device to the measurements of the fish. The disadvantage here again is that the end product is not fish in the form of fillets.
The patent U.S. Pat. No. 4,151,629 describes a machine which cuts the fish of lower quality from the bones, and then removes the fish of good quality from the remaining part of the bones. The way in which the remaining part of the bones. The way in which the latter happens does not form part of this patent.
U.S. Pat. No. 4,481,693 also describes an apparatus which presses the fish off the bones by having it conveyed between at least two pairs of rollers with elastic surfaces and turning in opposite directions. Here again, the fish does not retain its original structure, but is flattened by the roller surfaces and pressed in pieces from the bones.
Finally, there is another known process for removing the remaining fish from the bones after filleting, which is described in the patent DE-PS-3516623. This process is used with a machine consisting of hollow drums which in their wall surface are provided with small openings. The bones to which fish is clinging are pressed with great force against this wall through the fact that they lie on a conveyor belt which runs pressed against these drums. In this way the fish is pressed through the openings, apart from the bones, which are left behind on the conveyor belt and are carried along. The boneless fish pulp is then recovered from the hollow drums. This machine and process also produce an end product which is not fish which has retained its original structure in the end product, but a pulp.
According to the known processes and machines or appliances for removal of the remaining fish, after filleting from the bones, fish which has still retained its original structure and can be sold as fillets in the form of strips or slices is not therefore obtained in a single case.